Continuous Bright Light Research Articles

Effect of a light-darkness cycle on the body weight gain of preterm infants admitted to the neonatal intensive care unit

The Continuous bright light conditions to which premature infants are subjected while hospitalized in Neonatal Intensive Care Units (NICU) can have deleterious effects in terms of growth and development. This study evaluates the benefits of a light/darkness cycle (LDC) in weight and early hospital discharge from the NICU. Subjects were recruited from three participating institutions in Mexico. Eligible patients (n = 294) were premature infants who were hospitalized in the low-risk and high-risk neonatal units classified as stable. The subjects randomized to the experimental group (n = 150) were allocated to LDC conditions are as follows: light from 07:00 to 19:00 and darkness (25 lx) from 19:00 to 07:00. The control group (n = 144) was kept under normal room light conditions (CBL) 24 h a day. Main outcome was weight gain and the effect of reducing the intensity of nocturnal light in development of premature infants. Infants to the LDC gained weight earlier, compared with those randomized to CBL, and had a significant reduction in length of hospital stay. These results highlight those premature infants subjected to a LDC exhibit improvements in physiological development, favoring earlier weight gain and consequently a decrease in hospital stays. ClinicalTrials.gov; 02/09/2020 ID: NCT05230706.

Visual Comfort and Acute Alerting Effects of Diurnal Intermittent Bright Light

ABSTRACT Intermittent bright light during the night has shown to be able to generate circadian phase-shifting effects, suppress melatonin and induce alertness, but little attention has been devoted to the effects of diurnal intermittent bright light. Following a night of sleep restriction, forty participants were exposed in a counterbalanced within-subject design to an intermittent (100 lux – 1000 lux), a continuous dim (100 lux) and a continuous bright light condition (1000 lux) each lasting 90 min. Repeated assessments of self-reported sleepiness, cognitive performance and physiological arousal as well as subjective visual comfort were taken during each light condition. Results showed that alertness-related parameters were not significantly affected by the light conditions: neither the intermittent nor the bright condition improved alertness compared to the dim condition. Visual comfort was highest in the dim condition, followed by the intermittent and bright conditions respectively, even though the visualizations showed marked decreases in visual comfort during the bright light phases in the intermittent condition. The results illustrate the diversity in mechanisms underlying these visual experiences and neurobehavioral responses.

Bright light alone or combined with caffeine improves sleepiness in chronically sleep-restricted young drivers

BackgroundYoung drivers are over-involved in sleepiness-related crashes. The alerting effects of bright light offer a potential countermeasure for driver sleepiness, either replacing or in conjunction with current countermeasures such as the use of caffeine. MethodsThirty young (18–25) chronically sleep-restricted drivers drove in a simulator under randomized conditions of continuous bright light (‘Light,’ 500 nm, 230μw/cm2), caffeine (‘Caffeine,’ 100 mg caffeinated gum), or light and caffeine together (‘Light + Caffeine’), after driving under a placebo condition (‘Placebo,’ decaffeinated gum, 555 nm light, 0.3 μW/cm2) on three consecutive days. Using mixed-effects linear models, the associations between these conditions and physiological outcomes (EEG alpha and theta power, heart rate, and beat-to-beat intervals), driving performance (lateral lane and steering-related outcomes and lateral acceleration), and subjective sleepiness was assessed. ResultsRelative to Placebo, all conditions improved driving performance outcomes (P < 0.0001), with effects of Light + Caffeine equal to Light but greater than Caffeine. Light + Caffeine reduced EEG alpha power more than Light or Caffeine (P < 0.0006), but ECG outcomes were generally worse under all conditions relative to Placebo. Subjective sleepiness improved under the Light + Caffeine condition only (P < 0.0001). ConclusionsCombining bright light and caffeine enhances their alerting effects on lateral lane variability and subjective sleepiness. A bright light could be a practical alternative to caffeine for sleepy drivers who avoid caffeine. The alerting effects of bright light could alleviate chronic community-level mild sleep restriction and provide on-road benefits to reduce severe injuries and fatal sleepiness-related crashes.

Characterizing the temporal Dynamics of Melatonin and Cortisol Changes in Response to Nocturnal Light Exposure

We studied the dynamics of melatonin suppression and changes in cortisol levels in humans in response to light exposure at night using high-frequency blood sampling. Twenty-one young healthy participants were randomized to receive either intermittent bright (~9,500 lux) light (IBL), continuous bright light (CBL) or continuous dim (~1 lux) light (VDL) for 6.5 h during the biological night (n = 7 per condition). Melatonin suppression occurred rapidly within the first 5 min and continued until the end of each IBL stimuli (t1/2 = ~13 min). Melatonin recovery occurred more slowly between IBL stimuli (half-maximal recovery rate of ~46 min). Mean melatonin suppression (~40%) and recovery (~50%) were similar across IBL stimuli. Suppression dynamics under CBL were also rapid (t1/2 = ~18 min), with no recovery until the light exposure ended. There was a significant linear increase of cortisol levels between the start and end of each IBL stimulus. Under CBL conditions cortisol showed trimodal changes with an initial linear activating phase, followed by an exponential inhibitory phase, and a final exponential recovery phase. These results show that light exposure at night affects circadian driven hormones differently and that outcomes are influenced by the duration and pattern of light exposure.

The effects of intermittent light during the evening on sleepiness, sleep electroencephalographic spectral power and performance the next morning

Most studies on the effects of light exposure have been conducted with continuous light. The present study investigated the effects of intermittent light exposure on sleepiness, mood, electroencephalographic activity during sleep and performance the next morning. Fifteen volunteers were scheduled to come to the sleep laboratory to experience different lighting conditions: intermittent bright light, continuous bright light and continuous dim light. Subjective sleepiness and mood were assessed during light exposure, with electroencephalographic recording during sleep. After waking the next morning, participants filled out questionnaires and went through two cognitive tasks. The results revealed significantly lower ratings of sleepiness after intermittent light exposure, which is not different from the ratings in the continuous bright light condition, and an increase in vitality during later part of the evening and more beta activity during the first 90 minutes of sleep in the intermittent light condition, in comparison with the continuous dim light condition. However, both intermittent and continuous bright light exposure showed no difference from the continuous dim light condition in subjects' mood and cognitive functioning the next morning. The data indicated intermittent light during evening decreased sleepiness, had only minimal impact on mood in the evening, increased beta electroencephalographic activity during sleep, but had no significant influence on cognitive functioning the next morning.

Functional decoupling of melatonin suppression and circadian phase resetting in humans.

There is assumed to be a monotonic association between melatonin suppression and circadian phase resetting induced by light exposure. We tested the association between melatonin suppression and phase resetting in humans. Sixteen young healthy participants received nocturnal bright light (∼9500lux) exposure of continuous or intermittent patterns, and different durations ranging from 12min to 6.5h. Intermittent exposure patterns showed significant phase shifts with disproportionately less melatonin suppression. Each and every bright light stimulus in an intermittent exposure pattern induced a similar degree of melatonin suppression, but did not appear to cause an equal magnitude of phase shift. These results suggest that phase shifts and melatonin suppression are functionally independent such that one cannot be used as a proxy measure of the other. Continuous experimental light exposures show that, in general, the conditions that produce greater melatonin suppression also produce greater phase shift, leading to the assumption that one can be used as a proxy for the other. We tested this association in 16 healthy individuals who participated in a 9-day inpatient protocol by assessing melatonin suppression and phase resetting in response to a nocturnal light exposure (LE) of different patterns: (i) dim-light control (<3lux; n=6) or (ii) two 12-min intermittent bright light pulses (IBL) separated by 36min of darkness (∼9500lux; n=10). We compared these results with historical data from additional LE patterns: (i) dim-light control (<3lux; n=11); (ii) single continuous bright light exposure of 12min (n=9), 1.0h (n=10) or 6.5h (n=6); or (iii) an IBL light pattern consisting of six 15-min pulses with 1.0h dim-light recovery intervals between them during a total of 6.5h (n=7). All light exposure groups had significantly greater phase-delay shifts than the dim-light control condition (P<0.0001). While a monotonic association between melatonin suppression and circadian phase shift was observed, intermittent exposure patterns showed significant phase shifts with disproportionately less melatonin suppression. Each and every IBL stimulus induced a similar degree of melatonin suppression, but did not appear to cause an equal magnitude of phase shift. These results suggest unique specificities in how light-induced phase shifts and melatonin suppression are mediated such that one cannot be used as a proxy measure of the other.

The Acute Effects of Intermittent Light Exposure in the Evening on Alertness and Subsequent Sleep Architecture.

Exposure to bright light is typically intermittent in our daily life. However, the acute effects of intermittent light on alertness and sleep have seldom been explored. To investigate this issue, we employed within-subject design and compared the effects of three light conditions: intermittent bright light (30-min pulse of blue-enriched bright light (~1000 lux, ~6000 K) alternating with 30-min dim normal light (~5 lux, ~3600 K) three times); continuous bright light; and continuous dim light on subjective and objective alertness and subsequent sleep structure. Each light exposure was conducted during the three hours before bedtime. Fifteen healthy volunteers (20 ± 3.4 years; seven males) were scheduled to stay in the sleep laboratory for four separated nights (one for adaptation and the others for the light exposures) with a period of at least one week between nights. The results showed that when compared with dim light, both intermittent light and continuous bright light significantly increased subjective alertness and decreased sleep efficiency (SE) and total sleep time (TST). Intermittent light significantly increased objective alertness than dim light did during the second half of the light-exposure period. Our results suggested that intermittent light was as effective as continuous bright light in their acute effects in enhancing subjective and objective alertness and in negatively impacting subsequent sleep.

Glucocorticoid-Induced Leucine Zipper Protects the Retina From Light-Induced Retinal Degeneration by Inducing Bcl-xL in Rats

The aim of the present study was to investigate the neuroprotective effects of glucocorticoid-induced leucine zipper (GILZ) in a light-induced retinal degeneration model and to explore the underlying mechanisms. Intravitreal injection of recombinant GILZ-overexpressing lentivirus (OE-GILZ-rLV) and short hairpin RNA targeting GILZ recombinant lentivirus (shRNA-GILZ-rLV) was performed to up- and downregulate retinal GILZ, respectively. Three days after stable transduction, rats were exposed to continuous bright light (5000 lux) for 2 days. Retinal function was assessed by full-field electroretinography (ERG), and the retinal structure was examined for photoreceptor survival and death in rats kept under a 12-hour light:2-hour dark cycle following light exposure. The expression levels of retinal Bcl-xL, caspase-9, and caspase-3 were examined by Western blotting or real-time PCR at 1, 3, 5, and 7 days after light exposure. Exposure to bright light downregulated retinal GILZ in parallel with the downregulation of Bcl-xL and the upregulation of active caspase-3. Overexpression of retinal GILZ attenuated the decrease of Bcl-xL and the activation of caspase-9 and caspase-3 at 1, 3, 5, and 7 days after bright light exposure, respectively. GILZ silencing aggravated the downregulation of Bcl-xL induced by bright light exposure. Bright light exposure reduced the amplitude of ERG, increased the number of apoptotic photoreceptor cells, and decreased retinal thickness; and GILZ overexpression could attenuate all these effects. Overexpression of GILZ by OE-GILZ-rLV transduction protected the retina from light-induced cellular damage by activating antiapoptotic pathways.

Cycled light in the intensive care unit for preterm and low birth weight infants.

Potential benefits and harms of different lighting in neonatal units have not been quantified. • To determine effectiveness and safety of cycled light (CL) (approximately 12 hours of light on and 12 hours of light off) for growth in preterm infants at three and six months' corrected age (CA).• In separate analyses, to compare effects of CL with those of irregularly dimmed light (DL) or near darkness (ND), and effects of CL with those of continuous bright light (CBL), on growth in preterm infants at three and six months' CA.• To assess, in subgroup analyses, the effectiveness and safety of CL (vs control interventions (DL, ND and CBL)) introduced at different postmenstrual ages (PMAs) - before 32 weeks', at 32 weeks' and from 36 weeks' PMA - and to compare effectiveness and safety of CL for small for gestational age (GA) infants versus appropriately grown infants. We used the standard search strategy of the Cochrane Neonatal Review Group to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 12), MEDLINE via PubMed (1966 to January 2016), Embase (1980 to January 2016) and the Cumulative Index to Nursing and Allied Health Literature (CINAHL; 1982 to January 2016). We searched clinical trials databases, conference proceedings and reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials. Randomised or quasi-randomised trials of CL versus ND or CBL in preterm and low birth weight infants. We performed data collection and analyses according to the methods of the Cochrane Neonatal Review Group. We used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to assess the quality of evidence. We identified one additional study enrolling 38 participants for inclusion in this update, for a total of nine studies reporting on 544 infants. In general, the quality of the studies was low, mainly owing to lack of blinding and small sample sizes.Six studies enrolling 424 infants compared CL versus ND. No study reported on weight at three or six months. One study (n = 40) found no statistically significant difference in weight at four months between CL and ND groups. In another study (n = 62), the ratio of day-night activity before discharge favoured the CL group (mean difference (MD) 0.18, 95% confidence interval (CI) 0.17 to 0.19), indicating 18% more activity during the day than during the night in the CL group compared with the ND group. Two studies (n = 189) reported on retinopathy of prematurity (stage ≥ 3) and reported no statistically significant differences between CL and ND groups (typical risk ratio (RR) 0.53, 95% CI 0.25 to 1.11, I(2) = 0%; typical risk difference (RD) -0.09, 95% CI -0.19 to 0.01, I(2) = 0%). Two studies (n = 77) reported length of hospital stay (days) and noted a significant reduction in length of stay between CL and ND groups favouring the CL group (weighted mean difference (WMD) -13 days, 95% CI -23 to -2, I(2) = 0%; no heterogeneity). The quality of the evidence according to GRADE was low for this outcome. One study (n = 37) reported less crying at 11 weeks' corrected age (CA) in the CL group compared with the ND group (MD -0.57 hours/24 h, 95% CI -1.09 to -0.05). Tests for heterogeneity were not applicable.Three studies enrolling 120 infants compared CL versus CBL. Two studies (n = 79) reported significantly shorter length of stay in the CL group compared with the CBL group (WMD -16.5 days, 95% CI -26.2 to -6.8, I(2) = 0%; no heterogeneity). The quality of the evidence according to GRADE was low for this outcome. One study (n = 41) reported higher mean weight at three months' CA among infants cared for in the CL nursery (P value < 0.02) and a lower mean number of hours spent awake in 24 hours at three months of age (P value < 0.005). Data could not be entered into RevMan or GRADE. One study (n = 41) reported shorter time on the ventilator in the CL compared with the CBL group (MD -18.2 days, 95% CI -31.40 to -5.0). One study (n = 41) reported a shorter time to first oral feeding in the CL group (MD -6.8 days, 95% CI -13.29 to -0.31). We identified no safety issues. Trials assessing the effects of CL have enrolled 544 infants. No study reported on our primary outcome of weight at three or six months. Results from one additional study strengthen our findings that CL versus CBL shortens length of stay, as does CL versus ND. The quality of the evidence on both comparisons for this outcome according to GRADE was low. Future research should focus on comparing CL versus ND.

The Role of Pyruvate in Protecting 661W Photoreceptor-Like Cells Against Light-Induced Cell Death

ABSTRACTPurpose: Light is a requirement for the function of photoreceptors in visual processing. However, prolonged light exposure can be toxic to photoreceptors, leading to increased reactive oxygen species (ROS), lipid peroxidation, and photoreceptor cell death. We used the 661W mouse cone photoreceptor-like cell line to study the effects of pyruvate in protecting these cells from light-induced toxicity.Methods: 661W cells were exposed to 15,000 lux continuous bright light for 5 hours and incubated in Dulbecco’s modified eagle medium (DMEM) with various concentrations of pyruvate. Following light damage, cells were assessed for changes in morphology, cell toxicity, viability, and ROS production. Mitochondrial respiration and anaerobic glycolysis were also assessed using a Seahorse Xfe96 extracellular flux analyzer.Results: We found that cell death caused by light damage in 661W cells was dramatically reduced in the presence of pyruvate. Cells with pyruvate-supplemented media also showed attenuation of oxidative stress and maintained normal levels of ATP. We also found that alterations in the concentrations of pyruvate had no effect on mitochondrial respiration or glycolysis in light-damaged cells.Conclusions: Taken together, the results show that pyruvate is protective against light damage but does not alter the metabolic output of the cells, indicating an alternative role for pyruvate in reducing oxidative stress. Thus, sodium pyruvate is a possible candidate for the treatment against the oxidative stress component of retinal degenerations.

Chronically Alternating Light Cycles Increase Breast Cancer Risk in Mice

Although epidemiological studies in shift workers and flight attendants have associated chronic circadian rhythm disturbance (CRD) with increased breast cancer risk, causal evidence for this association is lacking. Several scenarios have been proposed to contribute to the shift work-cancer connection: (1) internal desynchronization, (2) light at night (resulting in melatonin suppression), (3) sleep disruption, (4) lifestyle disturbances, and (5) decreased vitamin D levels due to lack of sunlight. The confounders inherent in human field studies are less problematic in animal studies, which are therefore a good approach to assess the causal relation between circadian disturbance and cancer. However, the experimental conditions of many of these animal studies were far from the reality of human shift workers. For example, some involved xenografts (addressing tumor growth rather than cancer initiation and/or progression), chemically induced tumor models, or continuous bright light exposure, which can lead to suppression of circadian rhythmicity. Here, we have exposed breast cancer-prone p53(R270H/+)WAPCre conditional mutant mice (in a FVB genetic background) to chronic CRD by subjecting them to a weekly alternating light-dark (LD) cycle throughout their life. Animals exposed to the weekly LD inversions showed a decrease in tumor suppression. In addition, these animals showed an increase in body weight. Importantly, this study provides the first experimental proof that CRD increases breast cancer development. Finally, our data suggest internal desynchronization and sleep disturbance as mechanisms linking shift work with cancer development and obesity.

Loss of Melanopsin Photoreception and Antagonism of the Histamine H3 Receptor by Ciproxifan Inhibit Light-Induced Sleep in Mice.

Light has direct effects on sleep and wakefulness causing arousal in diurnal animals and sleep in nocturnal animals. In the present study, we assessed the modulation of light-induced sleep by melanopsin and the histaminergic system by exposing mice to millisecond light flashes and continuous light respectively. First, we show that the induction of sleep by millisecond light flashes is dose dependent as a function of light flash number. We found that exposure to 60 flashes of light occurring once every 60 seconds for 1-h (120-ms of total light over an hour) induced a similar amount of sleep as a continuous bright light pulse. Secondly, the induction of sleep by millisecond light flashes was attenuated in the absence of melanopsin when animals were presented with flashes occurring every 60 seconds over a 3-h period beginning at ZT13. Lastly, the acute administration of a histamine H3 autoreceptor antagonist, ciproxifan, blocked the induction of sleep by a 1-h continuous light pulse during the dark period. Ciproxifan caused a decrease in NREMS delta power and an increase in theta activity during both sleep and wake periods respectively. The data suggest that some form of temporal integration occurs in response to millisecond light flashes, and that this process requires melanopsin photoreception. Furthermore, the pharmacological data suggest that the increase of histaminergic neurotransmission is sufficient to attenuate the light-induced sleep response during the dark period.

Drift during overground locomotion in newly hatched chicks varies with light exposure during embryogenesis.

In an earlier study of newly hatched chicks we reported that continuous bright light exposure throughout incubation accelerated locomotor development and continuous dark exposure delayed it, compared to less intense, intermittent light exposure. Commonly studied gait parameters indicated locomotor skill was similar across groups. However, dark incubated chicks walked with a greater step width, raising the possibility of differences in dynamic balance and control of forward progression. In this study, we established methods to retrospectively examine the previously published locomotor data for differences in lateral drift. We hypothesized that chicks incubated in darkness would exhibit more drift than chicks incubated in light. Analyses identified differences in forward progression between chicks incubated in the two extreme light conditions, supporting the study's hypothesis. We discuss the significance of our findings and potential design considerations for future studies of light-accelerated motor development in precocial and nonprecocial animals.

Intermittent episodes of bright light suppress myopia in the chicken more than continuous bright light.

PurposeBright light has been shown a powerful inhibitor of myopia development in animal models. We studied which temporal patterns of bright light are the most potent in suppressing deprivation myopia in chickens.MethodsEight-day-old chickens wore diffusers over one eye to induce deprivation myopia. A reference group (n = 8) was kept under office-like illuminance (500 lux) at a 10∶14 light∶dark cycle. Episodes of bright light (15 000 lux) were super-imposed on this background as follows. Paradigm I: exposure to constant bright light for either 1 hour (n = 5), 2 hours (n = 5), 5 hours (n = 4) or 10 hours (n = 4). Paradigm II: exposure to repeated cycles of bright light with 50% duty cycle and either 60 minutes (n = 7), 30 minutes (n = 8), 15 minutes (n = 6), 7 minutes (n = 7) or 1 minute (n = 7) periods, provided for 10 hours. Refraction and axial length were measured prior to and immediately after the 5-day experiment. Relative changes were analyzed by paired t-tests, and differences among groups were tested by one-way ANOVA.ResultsCompared with the reference group, exposure to continuous bright light for 1 or 2 hours every day had no significant protective effect against deprivation myopia. Inhibition of myopia became significant after 5 hours of bright light exposure but extending the duration to 10 hours did not offer an additional benefit. In comparison, repeated cycles of 1∶1 or 7∶7 minutes of bright light enhanced the protective effect against myopia and could fully suppress its development.ConclusionsThe protective effect of bright light depends on the exposure duration and, to the intermittent form, the frequency cycle. Compared to the saturation effect of continuous bright light, low frequency cycles of bright light (1∶1 min) provided the strongest inhibition effect. However, our quantitative results probably might not be directly translated into humans, but rather need further amendments in clinical studies.

Bright light exposure reduces TH-positive dopamine neurons: implications of light pollution in Parkinson's disease epidemiology

This study explores the effect of continuous exposure to bright light on neuromelanin formation and dopamine neuron survival in the substantia nigra. Twenty-one days after birth, Sprague–Dawley albino rats were divided into groups and raised under different conditions of light exposure. At the end of the irradiation period, rats were sacrificed and assayed for neuromelanin formation and number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra. The rats exposed to bright light for 20 days or 90 days showed a relatively greater number of neuromelanin-positive neurons. Surprisingly, TH-positive neurons decreased progressively in the substantia nigra reaching a significant 29% reduction after 90 days of continuous bright light exposure. This decrease was paralleled by a diminution of dopamine and its metabolite in the striatum. Remarkably, in preliminary analysis that accounted for population density, the age and race adjusted Parkinson's disease prevalence significantly correlated with average satellite-observed sky light pollution.

Human phase response curve to a 1 h pulse of bright white light

The phase resetting response of the human circadian pacemaker to light depends on the timing of exposure and is described by a phase response curve (PRC). The current study aimed to construct a PRC for a 1 h exposure to bright white light (∼8000 lux) and to compare this PRC to a <3 lux dim background light PRC. These data were also compared to a previously completed 6.7 h bright white light PRC and a <15 lux dim background light PRC constructed under similar conditions. Participants were randomized for exposure to 1 h of either bright white light (n=18) or <3 lux dim background light (n=18) scheduled at 1 of 18 circadian phases. Participants completed constant routine (CR) procedures in dim light (<3 lux) before and after the light exposure to assess circadian phase. Phase shifts were calculated as the difference in timing of dim light melatonin onset (DLMO) during pre- and post-stimulus CRs. Exposure to 1 h of bright white light induced a Type 1 PRC with a fitted peak-to-trough amplitude of 2.20 h. No discernible PRC was observed in the <3 lux dim background light PRC. The fitted peak-to-trough amplitude of the 1 h bright light PRC was ∼40% of that for the 6.7 h PRC despite representing only 15% of the light exposure duration, consistent with previous studies showing a non-linear duration–response function for the effects of light on circadian resetting.

Kinematic analysis of overground locomotion in chicks incubated under different light conditions.

Domestic chicks walk within 3-4 hr after hatching following 21 days of incubation. However, differences in light exposure can vary incubation duration. Based on pilot studies, we predicted that there would be a positive relationship between incubation duration and locomotor competence at hatching. Embryos were incubated in one of three conditions that varied light duration and intensity, and overground locomotor performance was tested on the day of hatching. Chicks incubated in continuous bright light hatched 1-2 days earlier than chicks incubated in less or no light. Kinematic findings indicated that locomotor skill was similar across incubation conditions and led us to reject our hypothesis. We propose that light may accelerate locomotor development without adversely affecting skill. Our findings raise two important implications for future studies: whether light exposure accelerates locomotor circuit development; and/or it unmasks adaptive motor skill by accelerating development of other physiological systems.

Exposure to Bright Light Modifies HRV Responses to Mental Tasks during Nocturnal Sleep Deprivation

This study was intended to determine the effects of continuous bright light exposure on cardiovascular responses, particularly heart rate variability (HRV), at rest and during performance of mental tasks with acute nocturnal sleep deprivation. Eight healthy male subjects stayed awake from 21.00 to 04.30 hours under bright (BL, 2800 lux) or dim (DL, 120 lux) light conditions. During sleep deprivation, mental tasks (Stroop color-word conflict test: CWT) were performed for 15 min each hour. Blood pressure, electrocardiogram, respiratory rate, urinary melatonin concentrations and rectal temperature were measured. During sleep deprivation, BL exposure depressed melatonin secretion in comparison to DL conditions. During sleep deprivation, exposure to BL delayed the decline in heart rate (HR) for 4 h in resting periods. A significant increment of HR induced by each CWT was detected, especially at 03.00 h and later, under DL conditions only. In addition, at 04.00 h, an index of sympathetic activity and sympatho-vagal balance on HRV during CWT increased significantly under DL conditions. In contrast, an index of parasympathetic activity during CWT decreased significantly under DL conditions. However, the indexes of HRV during CWT did not change throughout sleep deprivation under BL conditions. Our results suggest that BL exposure not only delays the nocturnal decrease in HR at rest but also maintains HR and balance of cardiac autonomic modulation to mental tasks during nocturnal sleep deprivation.

New fluorescence parameters for monitoring photosynthesis in plants.

Chlorophyll fluorescence measurements have a wide range of applications from basic understanding of photosynthesis functioning to plant environmental stress responses and direct assessments of plant health. The measured signal is the fluorescence intensity (expressed in relative units) and the most meaningful data are derived from the time dependent increase in fluorescence intensity achieved upon application of continuous bright light to a previously dark adapted sample. The fluorescence response changes over time and is termed the Kautsky curve or chlorophyll fluorescence transient. Recently, Strasser and Strasser (1995) formulated a group of fluorescence parameters, called the JIP-test, that quantify the stepwise flow of energy through Photosystem II, using input data from the fluorescence transient. The purpose of this study was to establish relationships between the biochemical reactions occurring in PS II and specific JIP-test parameters. This was approached using isolated systems that facilitated the addition of modifying agents, a PS II electron transport inhibitor, an electron acceptor and an uncoupler, whose effects on PS II activity are well documented in the literature. The alteration to PS II activity caused by each of these compounds could then be monitored through the JIP-test parameters and compared and contrasted with the literature. The known alteration in PS II activity of Chenopodium album atrazine resistant and sensitive biotypes was also used to gauge the effectiveness and sensitivity of the JIP-test. The information gained from the in vitro study was successfully applied to an in situ study. This is the first in a series of four papers. It shows that the trapping parameters of the JIP-test were most affected by illumination and that the reduction in trapping had a run-on effect to inhibit electron transport. When irradiance exposure proceeded to photoinhibition, the electron transport probability parameter was greatly reduced and dissipation significantly increased. These results illustrate the advantage of monitoring a number of fluorescence parameters over the use of just one, which is often the case when the F(V)/F(M) ratio is used.

Dynamic resetting of the human circadian pacemaker by intermittent bright light.

In humans, experimental studies of circadian resetting typically have been limited to lengthy episodes of exposure to continuous bright light. To evaluate the time course of the human endogenous circadian pacemaker's resetting response to brief episodes of intermittent bright light, we studied 16 subjects assigned to one of two intermittent lighting conditions in which the subjects were presented with intermittent episodes of bright-light exposure at 25- or 90-min intervals. The effective duration of bright-light exposure was 31% or 63% compared with a continuous 5-h bright-light stimulus. Exposure to intermittent bright light elicited almost as great a resetting response compared with 5 h of continuous bright light. We conclude that exposure to intermittent bright light produces robust phase shifts of the endogenous circadian pacemaker. Furthermore, these results demonstrate that humans, like other species, exhibit an enhanced sensitivity to the initial minutes of bright-light exposure.